1. Field of the Invention
The present invention relates to an antenna apparatus and a portable radio set, and more particularly, is suitably applied to a cellular telephone.
2. Description of the Related Art
At present, such kind of the cellular telephone is miniaturized and reduced in weight for improvement of portability. Thus, in the antenna apparatus installed in the cellular telephone, a retracting/pulling type of whip antenna is actively developed. Such kind of the cellular telephone is exemplified by that configured as shown in FIGS. 1A and 1B.
The cellular telephone 1 of such configuration is configured by installing a whip antenna apparatus 3 in a housing case 2 made of such nonconductive material as a synthetic resin.
The antenna apparatus 3 has an antenna part 6 in which a telescopic antenna 4 made of a conductive, rod-like wire material and a helical antenna 5 formed by winding helically the conductive wire material are installed. The antenna part 6 is retractably and pullably installed along with a direction (hereafter, retracting direction,) in which the antenna part 6 is pushed into the inside of the housing case 2 shown by an arrow A in the top end 2A of the housing case 2, and on the contrary, a direction (hereafter, pulling direction,) in which pulled out from the inside of the housing case 2 to outside.
In the antenna part 6, a first feeding member 7 made of the conductive material and having a projected part 7A is electrically and mechanically connected to the bottom end of the telescopic antenna 4, and a connecting part 8 made of nonconductive material is mechanically connected to the top end of the telescopic antenna 4.
A second feeding member 9 made of the conductive material is electrically and mechanically connected to the bottom end of the helical antenna 5 and the second feeding member 9 is mechanically connected to the connecting part 8. According to this, in the antenna part 6 the telescopic antenna 4 and the helical antenna 5 are mechanically connected by the connecting part 8 and electrically insulated.
The telescopic antenna 4 is covered with an antenna cover 10 for the rod and the helical antenna 5 is retracted in the cap-like antenna cover 11 for the helix to prevent direct touch with a human body.
On the other hand, the inside of the housing case 2 contains a circuit substrate (not illustrated,) in which various circuit elements such as a transmission and reception circuit 12 and a matching circuit 13 are implemented, and a shield case (not illustrated,) made of the conductive material covering the circuit substrate, as a grounding member.
Inside the top end 2A of the housing case 2, an antenna feeding terminal 14, made of the conductive material, electrically connected to the matching circuit 13 is installed, and the antenna feeding terminal 14 is electrically connected to only any one of the telescopic antenna 4 or the helical antenna 5 in retracting and pulling out the antenna part 6.
Practically in the antenna apparatus 3, in pushing the antenna part 6 in, the antenna cover 11 for helix is pushed to a retracting direction to contact to the top end 2A of the housing case 2, the telescopic antenna 4 is retracted in the inside of the housing case 2 to house it and then, the second feeding member 9 is electrically connected to the antenna feeding terminal 14.
In the antenna apparatus 3, the helical antenna 5 is worked as the antenna by feeding the helical antenna 5 sequentially through the transmission and reception circuit 12, the matching circuit 13, the antenna feeding terminal 14, and the second feeding member 9.
Here in the antenna apparatus 3, the telescopic antenna 4 is adapted to no work as the antenna by electrically insulating from the antenna feeding terminal 14 in the connecting part 8.
In contrast, in the antenna apparatus 3, the second antenna cover 11 is pinched to pull to a pulling direction in a status in which the telescopic antenna 4 is retracted inside of the housing case 2 followed in pulling out the telescopic antenna 4 from the top end 2A of the housing case 2 to outside, and then the projected part 7A of the first feeding member 7 contacts with the antenna feeding terminal 14 to connect electrically the first feeding member 7 to the antenna feeding terminal 14.
In the antenna apparatus 3, the telescopic antenna 4 is worked as the antenna by feeding the telescopic antenna 4 sequentially through the transmission and reception circuit 12, the matching circuit 13, the antenna feeding terminal 14, and the first feeding member 7.
Here in the antenna apparatus 3, the helical antenna 5 is adapted to no work as the antenna by electrically insulating from the antenna feeding terminal 14 in the connecting part 8.
When the telescopic antenna 4 and the helical antenna 5 are worked respectively as antennae, impedance of the telescopic antenna 4 and the helical antenna 5 are matched to that of the unbalanced transmission line 16 using the matching circuit 13.
The shield case functions as a ground against various circuit elements and also functions as an electric shielding plate to prevent invasion of stray components of an electric wave of an external noise and the electric wave radiated from the antenna part 6 into various circuit elements implemented on the circuit substrate.
According to this, in the cellular telephone 1, in pulling the antenna part 6, the telescopic antenna 4 is pulled outside from the housing case 2, a transmission signal consisting of a high frequency signal is sent from the transmission and reception circuit 12 to the telescopic antenna 4 through the matching circuit 13, the transmission signal is sent to a base station (not illustrated) through the telescopic antenna 4, and also signal consisting of a high frequency signal, which is sent from base station and received by the telescopic antenna 4, is sent to the transmission and reception circuit 12 through the matching circuit 13.
In the cellular telephone 1, in retracting the antenna part 6, the telescopic antenna 4 is retracted inside the housing case 2 to prevent loss of portability thereof, in this status the transmission signal is sent from the transmission and reception circuit 12 to the helical antenna 5 through the matching circuit 13, the transmission signal is sent to the base station through the helical antenna 5, and also signal, which is sent from base station and received by the helical antenna 5, is sent to the transmission and reception circuit 12 through the matching circuit 13.
In the cellular telephone 1 with such configuration, for example, the unbalanced transmission line 15 comprising a microstrip line formed on the circuit substrate is installed, the telescopic antenna 4 or the helical antenna 5 is electrically connected to the transmission and reception circuit 12 sequentially through a hot side of the unbalanced transmission line 15 and the matching circuit 13, and also the ground side of the unbalanced transmission line 15 is grounded to the shield case.
Therefore, in the cellular telephone 1, as shown in FIG. 2A and 2B, when the telescopic antenna 4 or the helical antenna 5 is supplied an electric power from the transmission and reception circuit 12 sequentially through a hot side of the unbalanced transmission line 15 and the matching circuit 13 to work the telescopic antenna 4 or the helical antenna 5 as the antenna, a leak current i1 flows from the ground side of the unbalanced transmission line 15 to the shield case 16, showing that the shield case 16 works as the antenna.
However, in the cellular telephone 1, there is a problem that because the shield case 16 works as the antenna, when a user hold the housing case 2, a hand of the user covers over the shield case 16 through the housing case 2, and as a result, an antenna performances of the cellular telephone 1 deteriorates thereby decreasing in speech quality.
When the shield case 16 works as the antenna, if the user moves the housing case 2, held by the user""s hand, close to the user""s head, the head goes to the shield case 16 through the housing case 2 and thus, the antenna performances of the cellular telephone 1 further deteriorates resulting in decrease in speech quality.
Further, there is a problem that when the shield case 16 is moved close to the user""s hand or head, an electric power (so-called Specific Absorption Rate (SAR)) per unit time per unit mass absorbed by a certain site of a human body increases for amount thereof.
In view of the foregoing, an object of the invention is to provide an antenna apparatus and a portable radio set allowing greatly inhibiting decrease in speech quality.
The foregoing object and other objects of the invention have been achieved by the provision of an antenna apparatus which comprises a first antenna element installed retractably and pullably in a housing case, a fixed second antenna element making a pair with the first antenna element; an unbalanced transmission line feeding to the first and second antenna elements; and balanced-unbalanced converter means operating the balanced-unbalanced converter action between the unbalanced transmission line and the first and second antenna elements, wherein at the time of retracting and pulling the first antenna element, the first and second antenna elements are supplied an electric power from the unbalanced transmission line through the balanced-unbalanced converter means to work the first and second antenna elements as an antenna.
As a result, when the first and second antenna elements work as the antennae, it is prevented that the leaked current flows from the first and second antenna elements to the grounding member, to which the unbalanced transmission line is grounded, by the balanced-unbalanced converter action of the unbalanced transmission means through the unbalanced transmission line, and therefore, the work of the grounding member as the antenna can be prevented to allow greatly reducing deterioration of the performances of antenna near the human body.
Further the present invention provides an antenna apparatus which comprises a first antenna element installed retractably and pullably, fixed second and third antenna elements, an unbalanced transmission line feeding to the first and second and third antenna elements, balanced-unbalanced converter means operating the balanced converter between the unbalanced transmission line and the second and third antenna elements, wherein in retracting in the first antenna element, the first antenna element is electrically connected to the third antenna elements to make the first complex antenna to work as the antenna by feeding the second antenna elements and the first complex antenna from the unbalanced transmission line through the balanced-unbalanced converter means, and in pulling out the first antenna element, the first antenna element is electrically connected to the second antenna element to make the second complex antenna to work as the antenna by feeding the second complex antenna and third antenna element from the unbalanced transmission line through the balanced-unbalanced converter means.
As a result, when the second antenna element and the first complex antenna, and the second complex antenna and third antenna element are respectively worked as the antenna, a flow of a leaked current from the second antenna element or the first complex antenna, and the second complex antenna or third antenna element to the grounding member, to which the unbalanced transmission line is grounded, through the unbalanced transmission line is inhibited by balancing and unbalancing converter actions of the balanced-unbalanced converter means; and thus, action of the grounding member as the antenna is inhibited to allow greatly reducing deterioration of the performances of antenna near the human body.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.